I can't orgasm with my boyfriend

My sex life with my boyfriends started off magical. Unfortunately it's only gone down hill. I haven't had an orgasm with him in months. Even when i do it myself they're less awesome than what I'm used to. I don't know if there's something wrong with me or what, but it's causing a lot of strain on our relationship. When I try to talk to him about it I clam up because it's hard to put those thoughts/ feelings/ directions into words, and he starts crying because he feels bad that he can't please me. I'm starting to loose my patience. He's fine with me sleeping with girls without him, but I feel like my motives arnt right, searching somewhere else for something he should be able to provide. I don't know how to fix this